class Animal(object):
    pass
class Dog(Animal):
    def __init__(self,name) -> None:
        self.name = name
class Cat(Animal):
    def __init__(self,name) -> None:
        self.name = name
class Person(object):
    def __init__(self,name) -> None:
        self.name = name
        self.pet = None
class Employee(Person):
    def __init__(self, name,salary) -> None:
        super(Employee,self).__init__(name)
        self.salary = salary
class Fish(object):
    pass
class Salmon(Fish):
    pass
class Halibut(Fish):
    pass

rover = Dog("Rover")
satan = Cat("Satan")
mary = Person("Mary")
mary.pet = satan

frank = Employee("Frank",120000)
frank.pet = rover
flipper = Fish()
harry = Halibut()